There was an interesting article I read several days ago on this very problem from Ca.. It was suggested that it is a pig virus now affecting dogs , but it most likely is affecting dogs from contaminated vaccines(parvo) we are giving the dogs. We may be our own worst enemy.If we feed more wholesome food and less medicines we might be better off. I know new diseases are growing each year , I think back over the years how many dogs we raised and hunted for years and never wormed them or gave any shots and they made it fine. I had one old dog that lived to be eighteen years old and hunted until almost fourteen. I don't remember worming or giving a shot to him.